Solenoid operated directional control cartridge valves can be fitted directly into the hydraulic power pack central manifold. 3/4"UNF cartridge valves are an industry standard 08 size. Normally closed and open types give two different functions. The Normally closed valve holds pressure within the P port and when energized this is released to the tank, thus lowering a tipper truck or tail lift. Normally open works in the opposite way, allowing oil to the tank until the coil is energized, this is useful to un-load the main pump or release a hydraulic brake.